As an example of a magneto-optical memory device, a magneto-optical disk provided with a substrate whereon a first dielectric film, a recording-reproduction film, a second dielectric film, a reflecting film, and an overcoat film are laminated in this order is known.
For the recording-reproduction film, a thin film of rare-earth transition metal alloy (RE-TM) having perpendicular magnetic anisotropy such as DyFeCo, TbFeCo, or GdTbFe is used.
When recording is to be carried out on the magneto-optical disk, light such as a laser beam is projected onto the recording-reproduction film. As a result, temperature of the portion irradiated with the light is raised, and the coercive force (Hc) at the portion becomes small. Then, the magnetization direction of the portion is arranged in the magnetization direction of an external magnetic field, thereby recording information in a form of recording bits.
When reproducing is to be carried out from the magneto-optical disk, a linearly polarized light is projected onto the recording bits recorded on the recording-reproduction film, and the information is reproduced utilizing the Kerr effect (the rotation angle of the linearly polarized light varies depending on the magnetization direction of the recording bits). When adopting the above reproducing method, the recording bits recorded with an interval smaller than the diameter of the light spot on the recording-reproduction film cannot be reproduced.
In order to counteract the above problem, recently, a magneto-optical recording disk which enables recording bits recorded with an interval smaller than the diameter of the light spot has been proposed. Namely, even when a plurality of recording bits are recorded in the area where the light spot is formed, each of the recording bits can be reproduced (see Jpn. J. Appl. Phys. Vol. 31 (1992) Pt. 1, No. 2B).
As shown in FIG. 27, the magneto-optical disk is mainly composed of a substrate 81 whereon a read-out film 83 and a recording film 84 (magnetic thin film with a perpendicular magnetization) are laminated. The recording film 84 has high coercive force at room temperature. The coercive force of the read-out film 83 is set smaller than the coercive force of the recording film 84. When temperature of the reproducing portion of the read-out film 83 is raised, the magnetization direction of the read-out film 83 is arranged in the magnetization direction of the recording film 84. Namely, by the exchange coupling force exerted between the read-out film 83 and the recording film 84, the magnetization of the recording film 84 is copied to the read-out film 83.
The recording on the magneto-optical disk is carried out through the generally adopted magneto-optical recording method. When the recording bits recorded on the magneto-optical disk are to be reproduced, the read-out film 83 is required to be initialized beforehand so that the magnetization direction of the read-out film 83 is arranged in a predetermined direction (upward in the figure) by applying thereto the subsidiary magnetic field from a subsidiary magnetic field generation device 86. Then, the reproduction-use beam is projected onto the read-out film 83 through a lens 98, and the temperature of the portion irradiated with the beam is raised. As a result, the magnetized information recorded on the recording film 84 is copied to the read-out film 83.
In this way, the magnetized information is copied only to the central portion of the light spot of the reproduction-use light beam. As a result, the recording bits recorded with an interval smaller than the light spot can be reproduced.
However, in the above conventional arrangement, when reproducing is to be carried out, the magnetization of the read-out film 83 must be initialized beforehand by the subsidiary magnetic field generation device 86. Therefore, the above arrangement presents the problem that the magneto-optical recording and reproduction device becomes larger in size.